Two independent methods of characterizing and quantitating ACTH from clinical samples are being developed, a classical radioimmunoassay with materials supplied by the NIAMDD and a bioassay, using as an endpoint the corticosterone production of isolated rat adrenal fasciculata cells. Both assays have been found to be sensitive enough for human use and to have specificity which is suitable. An extraction procedure is being developed and is the final step in completing both assays. In addition gel chromatography and ion exchange chromatography are being used to characterize the ACTH. Also, the columns are being used to prepare biologically active 125 I-labeled ACTH for receptor studies.